Optical measurement device and related process

ABSTRACT

An instrument and related process for measuring color, shade, gloss, shape and/or translucence of a tooth. First, the instrument uses searchlight illumination to illuminate a tooth with constant irradiance. Second, the instrument uses colorimetric imaging to collect time-separated frames of different wavelengths of light reflected from a tooth and to combine those frames into a color image. Third, the instrument includes a sanitary shield to establish a reference color and a predetermined distance to a target tooth. Fourth, the instrument provides line-of-sight viewing so an operator may simultaneously view a display of the image on the instrument and the object being measured. Fifth, the instrument is impervious to pollutants because it incorporates a sealed measurement window. Sixth, optical measurements of a tooth taken by a dentist are compared to optical measurements of a prosthetic restoration for that tooth to confirm satisfactory matching of optical characteristics of the tooth and restoration.

This is a division of U.S. application Ser. No. 10/236,529, filed Sep.6, 2002 (now U.S. Pat. No. 6,867,864), which is a division of pendingU.S. application Ser. No. 09/733,162, filed Dec. 8, 2000, which claimsbenefit of U.S. Provisional Application No. 60/169,638, filed Dec. 8,1999, all of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

The present invention relates to instruments for measuring opticalcharacteristics—for example color, translucency, and/or gloss—of objectsand, more particularly, to such instruments for use in dentalapplications.

The determination of shade or color of an object is a process that isfrequently performed in the field of dentistry. To perform dentalrestorations of a damaged tooth, a dentist visually compares the colorof the tooth to be replaced with an assortment of shade tabs. Theseshade tabs are physical tabs representing the color of commerciallyavailable restorative material, such as ceramics. The tabs include theexact specification of materials needed to produce a restorative toothwith the shade of the original tooth as determined by the dentist'svisual comparison. Once the dentist finds a shade tab that matches thecolor of the tooth, or remaining adjacent teeth in some cases, he is ina position to manufacture the required restoration. This process,however, is very time consuming and quite subjective, and frequentlyresults in poorly shaded restorations.

In the field of dentistry, intraoral cameras are frequently used toacquire images of teeth and determine treatment plans for cavities andother mechanical reconstruction. These cameras are designed to beversatile and able to collect measurements in tight places often foundin the mouth; however, they do not preserve the color fidelity—that is,they do not collect the true color—of the object measured.

Some dentists attempt to use intraoral cameras to assist in the shadedetermination process. Unfortunately, conventional intraoral camerassuffer two problems: distance sensitivity due to illumination geometryand color discrimination error due to sensor limitations.

With regard to the first problem, intraoral cameras typically usefiberoptic illumination to reduce the size of the handpiece. Such adevice is disclosed in U.S. Re. Pat. No. 36,434 to Hamlin et al,reissued Dec. 7, 1999. The goal of Hamlin, and most intraoral cameras,is to provide a small measuring tip on a handpiece that can be used toprobe hard to reach areas in a mouth. Although fiber-optic illuminationis useful for providing high levels of illumination and is compatiblewith small measuring probe tips, a drawback of any smallillumination-source that illuminates a larger area is that the projectedbeam must be divergent light. The intensity of a divergent beam isgoverned by the inverse square law given below:

$\begin{matrix}{I = \frac{D^{2}}{\left( {D + {\Delta\; D}} \right)^{2}}} & (1)\end{matrix}$where I is intensity, D is the distance from the illumination source,and ΔD is an increase in distance D from the light source. The conceptof Equation 1 is illustrated in FIG. 1, where fiber optic source 115projects illumination flux 112 to distances D and D plus ΔD. There, theintensity of flux 112 at distance D, according to Equation 1, is greaterat distance D from light source 115 than at a distance D plus ΔD.

It is known that when the distance change to the illumination source issignificant with respect to the distance to the source, the illuminationoutput varies significantly, creating what is called non-uniformillumination. Particularly with objects positioned close to the fiberoptics, certain regions of the object are non-uniformly illuminatedbecause the light from the illumination source rapidly diffuses as ittravels away from the source. Moreover, when multiple sources of lightare used to illuminate an object, the object may be non-uniformlyilluminated in different regions.

An example of non-uniform illumination of the surface of an object isunderstood with further reference to FIG. 1. As depicted there, a curvedsurface of a tooth T, slightly exaggerated for purposes of discussion,is illuminated within flux 112 projected from light source 115. Regionof the tooth 113, lies distance D from light source 115, and region 114,lies distance D plus ΔD from the light source 115. As explained above,the intensity of light is greater at distance D than at D plus ΔD.Accordingly, regions 113 and 114 are not illuminated with the sameintensity of light, that is, illumination is non-uniform. Sensorssensing light reflected from tooth T will collect inconsistent colorinformation from these regions.

An example of non-uniform illumination of regions of an object with amultiple fiber optic light sources is illustrated in FIG. 2. Exemplaryfiber optic light sources 120 and 122 project light fluxes 130 and 140to illuminate the tooth T These light fluxes reflect from the tooth andare collected by an image sensor not shown for the sake of simplicity.As can be seen, tooth region 122 is illuminated primarily by light flux140, but region 124 is illuminated by a combination of light fluxes 130and 140. Of course, this illumination is three-dimensional even thoughit is depicted here in only two dimensions. Further, if more fiber opticlight sources are added, the tooth is subdivided into even more regionsof different illumination overlap. Given this non-uniform illumination,a color sensor, sensing the light reflected from the tooth, willinvariably collect inconsistent color information from region to region.For example, what is sensed as “lighter shade” in region 122 may besensed as “darker shade” in region 124 due to the non-uniformillumination.

With non-uniform illumination, conventional intraoral cameras criticallyrely on illumination source positioning which can not be maintained inpractical use. This results in significant errors affecting tooth shadedetermination.

Other devices, specifically designed for tooth shade determination, havebeen proposed that use bi-directional fiber optic illumination. Such amethod is described in U.S. Pat. No. 6,038,024 to Berner, issued Mar.14, 2000. A limitation of this method of illumination is that theilluminant intensity is maximized at the intersection of the twoprojected beams. Often, significant portions of the measured area arenot illuminated by both beams and hence have a lower and unpredictableillumination value.

Berner's non-uniform illumination is depicted in FIG. 3. A fiber opticbundle 150 is supplied with light at one end. Prior to arriving at theprobe tip, the bundle is bifurcated, or divided into two bundles 152 and154. The bundles are mechanically aimed at the target tooth T in somefixed angularity. Collimating lenses 156, 158 are often added in thepath of illumination between the fiber optic bundle and the target T tolower distance sensitivity of illumination output. Each bundle generatesa light flux 162 and 164 projected onto tooth T from two directions withcollimating lenses 156, 158. As can be seen, fluxes 162 and 164intersect on tooth T resulting in the intensity in region 169 beinggreater than the intensities in regions 167 and 171 because thoseregions 167 and 171, and other peripheral regions, are each illuminatedby light fluxes 164 and 162 individually. The fluxes reflected from thetooth T are not shown for simplicity.

Given this non-uniform illumination, a color sensor, sensing the lightreflected from the tooth, will invariably collect inconsistent colorvalue information from region to region. For example, what is sensed as“lighter shade” in region 167 may be sensed as “darker shade,” in region169 due to the non-uniform illumination. Moreover, with multiple lightsource paths, gloss artifact potential is increased. Where glareartifacts exist, the color of the target is washed out by the image ofthe light source itself rather than the desired tooth subject.

In addition to non-uniform illumination, today's intraoral camerasutilize color filter array (CFA) image sensors that frequentlycontribute to inaccurate color measurement because the filter array isapplied to the image. Many intraoral cameras include color filter arrayssuch as red, green and blue (RGB) arrays, and cyan, magenta, yellow andgreen (CMYG) arrays, to name a few. Generally, these color filter arraysare made up of a multitude of adjacent elements called “pixels” (i.e.,picture elements). Each pixel measures only the bandwidth of light it isdesigned to collect. Therefore, in a region of a image corresponding toa pixel, only the bandwidth of light specific to that pixel isdisplayed, even though the object measured may include other colors inthat region.

The operation of and problems associated with color filter arrays aremore readily understood with reference to a particular array. A fewpixels of a CFA RGB sensor are illustrated in FIG. 4 as R, B, G. TheseR, G, and B pixels collect, capture or sense light corresponding to red,green and blue wavelengths impinging on the sensor respectively. The RGBsensor converts these collected wavelengths into electronic data andpasses this data to a processor for display of a color image of thetooth on a monitor. Although RGB sensors offer a means to collect colordata for a tooth, that data often is not an accurate representation ofthe true color or distribution of color on the tooth.

CFAs do not accurately measure color primarily because of two factors:pixel spacing separation and poor color fidelity. First, the pixelspacing separation factor may be understood with reference to the RGBsensor in FIG. 4. Each individual R, G, and B pixel in the RGB array 100collects only one bandwidth of light reflected from a point on a tooth,for example, only red, only green, or only blue. Thus, when toothsections 101 and 102 are illuminated and reflect light toward the RGBarray and that light is detected by the corresponding G and B pixelsrespectively, only green bandwidths are collected by the green pixel andonly blue bandwidths are collected by the B pixel. Even though section101 actually may be blue, green, red, yellow or any other color of thespectrum, and consequently reflect the associated bandwidths, only thegreen bandwidth, if any, is detected by pixel G in section 101.Similarly, section 102 may be green or any other color, but those colorsare not detected by the B pixel because blue is the only bandwidth thatit can collect.

Accordingly, RGB sensors collect only one bandwidth for each point onthe tooth even though that point may reflect many bandwidths. As aresult, any measurement data for that point will include only dataselectively collected by the R,G, or B pixel associated with that point.Moreover, prosthesis manufactured from this measurement data collectedwith an RGB sensor will not accurately reflect the true color of eachpoint on the tooth. This phenomenon applies to all CFA sensors.

The second factor affecting color measurement is poor color fidelity ofCFAs. The mass market for color sensors, in particular CFAs, is consumerelectronics and video applications. The goal of such devices is toprovide good image resolution, high image acquisition speed andreasonable color fidelity as needed for broadcast and personal imagingapplications. CFAs are designed to be inexpensive to manufacture, toprovide direct acquisition of RGB data and to provide reasonable lowlight performance. These design goals come at the cost of colorfidelity. More specifically, today's RGB CFA collects selectedwavelengths of light impinging on them, but they also incidentallycollect unwanted wavelengths in the process. For example, a blue pixelof an RGB array is coated with a polymer that is designed to (a) allowonly light of blue bandwidths to be transmitted through thepolymer—acting like a filter—and sensed by that pixel, and (b) attenuateall other wavelengths, that is, prevent them from being sensed by thatpixel. Typical CFA filters attenuate unwanted wavelengths by only1/10^(th) of the value of the maximum transmittance of the filter. Thislack of rejection of light outside of the wavelengths of interestdegrades color fidelity to an unacceptable level for accurate colormeasurement.

Due to signal detection problems caused by pixel spacing and poor colorfidelity, CFA-type sensors are not accurate enough for satisfactorydetermination of tooth shade.

Currently, most intraoral cameras include a sheath to cover theilluminating portion and/or image sensor. Conventional sheaths aredisposable, so that they may be replaced if they accidentally orintentionally come in contact with a patient's mouth. By replacing asheath between measurements on different patients, a dentist may preventspread of contaminants, such as infectious agents, from a first patientto subsequent patient. Although these protective sheaths prevent spreadof contaminants, their functionality is limited exclusively to thissanitary purpose.

Conventional intraoral cameras also include a handheld probe that adentist inserts into a patient's mouth and collects color images with.Via a cable, the probe transmits collected color measurement to acomputer that subsequently processes the measurements to create imagesand displays those images on a monitor for the dentist to view. Thedrawback in collecting images of a tooth with these conventional probesis that the dentist must look back and forth from the probe to themonitor to insure the probe is positioned over the tooth to obtain thedesired image on the monitor. This, of course can cause unneededfrustration in aligning the probe to collect measurements of the tooth.

In many instances, intraoral cameras or parts thereof intentionally oraccidentally come into contact with a patient's intraoral cavity therebytransmitting contaminants including infectious agents, saliva and/orfood debris to the device. In addition to using sanitary sheaths asdiscussed above, operators of prior art intraoral cameras frequentlyclean or sterilize the cameras. This is often a tedious task, as thecameras include a plurality of buttons that are difficult to cleanaround and/or fiber optic bundles that are nearly impossible tosterilize without damaging the optical characteristics of the fibersbecause sterilization agents enter the fiber optics and degradeillumination or sensing capabilities. Accordingly, prior art camerausers must exercise time-consuming care in operating and cleaning thesecameras.

Typically, a dentist makes a shade determination visually using shadetabs. A prescription describing the restoration location and shade issent to the dental laboratory. There, a technician attempts to duplicatethe tooth shade to make prosthesis from available ceramic or syntheticmaterials. Once the prosthesis is manufactured, it is sent back to thedentist for installation in the patient.

Only after placing the prosthesis in proximity to the patient's damagedtooth and/or surrounding teeth can the dentist determine if theprosthesis is an acceptable duplicate of the damaged tooth. Of course,if the prosthesis does not match properly, the dentist must have asecond prosthesis made by a lab incorporating his suggestedmodifications. A second shade determination of the tooth may even berequired. The second prosthesis must also be compared by the dentist tothe damaged tooth to insure a proper match. This process is very costlyif multiple prosthetic replacements must be produced to create asatisfactory match. Moreover, this process consumes the time of patientswho may come in for repeated visits before a matching prosthesis iscreated.

SUMMARY OF THE INVENTION

The aforementioned problems are overcome by the present inventionwherein an optical measurement instrument uses searchlight illuminationand colorimetric imaging to collect optical characteristic measurementsof objects such as teeth.

The present invention uses searchlight illumination to uniformlyilluminate an object when measuring the optical characteristics, such ascolor, shade, translucence, shape and/or gloss of that object.“Searchlight illumination” refers to illumination wherein all points ofthe object measured are illuminated with constant irradiance.Searchlight illumination is readily understood with reference to FIG. 5.An illuminator 80 includes light source 520 and lens 528, which ispreferably an achromatic doublet lens. Any type of uniform and diffuselight source may be substituted for the illuminating integrating sphere518. The preferred source provides a spectrum of light that iscontinuous in radiant power across the visible wavelength range. Lightof this type may be generated from an incandescent source filteredthrough heat absorbing glass. The lens 528 is set to a distance of thefocal length of the lens from the light source 520 so that the lensprojects light rays 530 and 540 on the tooth T. Accordingly, the entireregion 522, that is the entire side of the tooth being measured isuniformly illuminated with the constant irradiance of rays 530 a and 540a.

Searchlight illumination offers significant benefits in the opticalmeasurement context. First, image sensors used with searchlightillumination consistently collect optical information from lightreflected from an object because the illumination is uniform over theobject. Second, searchlight illumination does not vary significantlywhen the distance between the object and the instrument is increased aswith conventional intraoral camera illumination systems. Accordingly,the positioning of the illumination source from the tooth may be variedwithout significantly sacrificing consistent optical informationsensing. Third, with searchlight illumination, the occurrence of glareartifacts is diminished; and the optical characteristics of the objectmeasured by a sensor are not washed out by this glare.

In another aspect of the invention, the preferred optical measurementinstrument implements colorimetric imaging to measure the opticalcharacteristics of objects. Colorimetric imaging is a process whereinmultiple time-separated measurements, or “frames,” of specific ranges ofbandwidths of light in the visible spectrum are collected for all pointson an object measured with an image sensor, preferably a monochromeimage sensor. These frames are then combined to form a color image ofthe measured object, incorporating each collected frame and consequentlyeach collected bandwidth. When combined, every point on each frame isaligned with its corresponding points on each other frame. When all theframes are combined, the resultant image depicts every point on thetooth and every bandwidth collected for that point on the tooth.

In the preferred embodiment, light reflected from an object, alsoreferred to herein as “radiant flux,” is sequentially transmittedthrough multiple filters that selectively absorb some wavelengths andtransmit others to a monochromatic image sensor. These filterspreferably have well controlled bandpass functions, that is, the filtersallow specifically desired wavelengths of light to be transmitted to thesensor. These filters are specified by spectral transmittance curves.Preferably, the filters significantly attenuate wavelengths outside ofthe specified band pass function. Accordingly, these filters have veryhigh color fidelity. Of course, depending on the application, theattenuation and transmission of certain wavelengths may be varied asdesired.

In the preferred embodiment, each of these filters transmits a preferredrange of bandwidths corresponding to Commission Internationaledei'Eclairage (“CIE”) tristimulus value bandwidths, for example, X, Y, Zand X′ tristimulus bandwidths. Trisumulus values relate to the spectralsensitivity of the human eye. Instruments that measure using thesebandwidth shapes correlate highly with data generated from human colorperception. In this manner, the monochromatic image sensor collects onlyone bandwidth or range of bandwidths at time. These individual,collected bandwidths are recorded as frames by the image sensor,converted to electric signals and transferred to a processor. Theprocessor combines and aligns these frames to form an image includingall the collected bandwidths for every point on the image.

The problems inherent in the RGB sensors of prior art intraoral cameras,specifically pixel spacing separation and poor color fidelity, areeliminated with colorimetric imaging. Multiple bandwidths and the colorsassociated therewith are collected for each point on the tooth, ratherthan a single red, or green, or blue bandwidths. Additionally, becausecolorimetric imaging uses monochrome sensors having non-colored pixels,no defects attributable to poor color fidelity affect the collection ofbandwidths. The resultant image created with colorimetric imaging is anextremely accurate representation of the true colors of the tooth to bereplaced. Moreover, dental prosthesis created from this color data ismuch more likely to match the color of the replaced tooth.

In another aspect of the invention, the optical measuring instrumentincludes a multi-functional sanitary shield. In addition to preventingcontamination from spreading from one patient to the next, these shieldsare of a predetermined length to establish an optimal distance between(a) the illumination source and/or (b) the image sensor, and the objectmeasured. The shield also includes a reference strip, preferablyoff-white, that is included in images collected by the opticalmeasurement instrument. The value of measurement associated with thisreference strip in collected images is compared during measurement tovalues acquired during instrument calibration. This comparison providesa method of determining not only the lamp intensity variation—and theillumination in general—but also provides a method to determine changesin lamp color temperature. Both of these values are used to provideaccurate color measurement data from the imaged tooth. In a preferredembodiment, the disposable shield is also constructed from an opaquematerial that prevents any ambient light from entering the shield andaffecting any measurements made by the optical measurement instrument.

In another aspect of the invention, the optical measurement instrumentis configured so that an operator of the instrument may view an image ofan object on a display, preferably a liquid crystal display (LCD), alonga line of sight that is the same as the line of sight along which animage sensor of the instrument collects an image of the object.Accordingly, the operator views the object from the same perspective asthe image sensor collects the image of the object. With this “line ofsight” viewing, the operator may align the image sensor of the opticalmeasurement instrument so that it collects the exact image she desiressimply by looking at the LCD. She need not look at the object shedesires to measure and then turn her head to view a separate monitor toconfirm that what she expected the sensor to collect is what is actuallycollected.

In another aspect of the invention the optical measurement instrumentincludes a sealed housing that facilitates sanitation and cleanup. Thehousing is sealed at all joints of adjoining panels that make up thehousing. An LCD display is sealably incorporated into the housing.Preferably the display is touch sensitive so that buttons and theircorresponding apertures in the housing body are eliminated. The housingbody also includes an aperture through which optical measurementillumination and sensing is performed. This aperture is covered with atransparent window that is sealably mounted to the housing. Because thehousing and this aperture are sealed from the environment, the sensitiveillumination and sensing instrumentation therein is not subject topollutants such as dust or sanitizing or cleaning agents and the like.

In another aspect of the invention, the optical characteristics of amanufactured prosthetic restoration is compared to the opticalcharacteristics of the damaged tooth that the restoration is to replacebefore the restoration is shipped to a dentist for installation in apatient's mouth. In the preferred embodiment, a dentist collects animage of a damaged tooth or remaining surrounding teeth with an opticalmeasurement instrument. This image is electronically forwarded to adental prosthesis manufacturer who subsequently creates a prosthesis, orrestoration, to replace the damaged tooth. Before shipping theprosthesis to the dentist, however, the manufacturer uses her ownoptical measurement instrument to collect an image of the prosthesis,and compares this image to the original image of the tooth. Duringcomparison, the manufacturer insures that the optical characteristics ofthe image of the prosthesis accurately duplicate the opticalcharacteristics of the image of the tooth. If characteristics aresatisfactory, the manufacturer ships the prosthesis to the dentist forinstallation in the patient's mouth. If the characteristics of theprosthesis do not satisfactorily match the damaged tooth or surroundingteeth, a new prosthesis is made, and its image is collected and comparedto the image of the damaged tooth or surrounding teeth. This process maybe repeated until a satisfactory prosthesis is created.

By insuring that the optical characteristics of a prosthetic restorationaccurately match the optical characteristics of the damaged tooth,dentists and patients can be assured that when the prosthesis arrivesfrom the manufacturer, it will be a satisfactory match of the damagedtooth and acceptable for installation in the patient's mouth.

In the discussion herein, reference is made to an “object,” “material,”“surface,” etc., and it should be understood that in general such adiscussion may include teeth, dentures, gums, or other prosthesis orrestorations, dental filling material, dental adhesives or the like orother dental objects as well as any other objects or materials as the“object,” “material,” “surface,” etc.

These and other objects, advantages and features of the invention willbe more readily understood and appreciated by reference to the detaileddescription of the preferred embodiments and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of the intensity of light projected from a fiberoptic illumination source of the prior art;

FIG. 2 is a side view of non-uniform illumination from a fiber opticillumination source of the prior art;

FIG. 3 is a side view of non-uniform illumination from a bifurcatedfiber optic illumination source of the prior art;

FIG. 4 is a perspective view of an RGB sensor of a prior art intraoralcamera collecting color data from a tooth;

FIG. 5 is a side view of a the generic searchlight illuminator of thepresent invention;

FIG. 6 is an exploded perspective view of an optical measurementinstrument;

FIG. 7 is a side view of a region of constant irradiance;

FIG. 8 is a side view of a modified region of constant irradiance usedin searchlight illumination;

FIG. 9 is a graph comparing illumination intensity of various lightsources as relative distance to an object is varied;

FIG. 10 is a sectional view of a preferred illuminator;

FIG. 11 is an exploded perspective view of an imaging subsystem;

FIG. 12 is a flow chart of an alignment process of the imagingsubsystem;

FIG. 13 is an end view of a sanitary shield;

FIG. 14 is a side elevation view of the sanitary shield in use;

FIG. 15 is a side view of a line of sight feature of the opticalmeasurement instrument;

FIG. 16 is a perspective view of the line of sight feature;

FIG. 17 is a perspective of a sealed window of the optical measurementinstrument; and

FIG. 18 is a perspective view of the optical measurement instrument in adocking station.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

With reference to FIG. 6, the preferred embodiment of the opticalmeasurement instrument 10 will now be described. The optical measurementinstrument 10 generally includes a housing 12, display 18, processor 20,imaging subsystem 50, illuminator 80, power source 90, and sanitaryshield 300. The housing 12 includes subparts 12 a and 12 b to allow easyassembly and access to the internal components housed therein. Thehousing subparts seat and seal together to create a housing thatprevents contamination of sensitive internal components by dust andchemicals. The housing 12 may be constructed of any material; however, alight, easily cleanable, synthetic material, such as plastic, ispreferred for handheld use and shock resistance.

The display 18 and the processor 20 may be separate or integrated as aunit as depicted. The display 18 is preferably a liquid crystal display(LCD). The LCD preferably has a touch screen interface to provide imagecontrol, data display and targeting feedback through a video viewfinder.As will be appreciated, any other display screens may be used.Alternatively, the optical measuring instrument may be connected via acable (not shown) to a monitor or display (not shown) that is separatefrom the instrument for displaying images collected by the instrument.

In the preferred embodiment, the processor 20 is in electricalcommunication with the display 18, illumination assembly 80, and imagingsubsystem 50. This processor is capable of processing digitized datacollected from the imaging subsystem 50 and formatting it so that animage of that digitized data is output to the display screen 18. Theprocessor preferably formats digitized measurements such as tristimulusvalue bandwidths collected by the image sensor 56 to form an image ofthe object measured on the display 18.

The processor 20 includes port 22 to connect to the instrument 10 todocking station, described in further detail below, to download imagesand/or data collected by the optical measuring instrument to a computerconnected to the docking station for further analysis. Port 22 is alsoin electrical communication (not shown) with power source 90 so that thepower source may be recharged when the instrument 10 is in its dockingstation.

Illuminator 80 is preferably mounted in the housing 12 in fixed relationto the imaging subsystem 50. This is accomplished via connectors 82 thatmay be of any configuration to hold the two assemblies in fixedrelation. The fixed relation is preferably configured so that theilluminator 80 illuminates an object, such as a tooth, with light at aselected angle and the light reflected from the tooth is collected bythe imaging subsystem 50 at a selected angle. In a preferred embodiment,the illuminator illuminates an object in an angle 18 degrees off normaland the imaging subsystem 50 collects light reflected from the object atan orientation normal to the object's surface. This configuration helpsto reduce glare artifacts.

Of course, the illuminator 80 and imaging subsystem 50 may be configuredin any angular configuration depending on the desired application. Forexample, the illumination and image capturing may be done both normal tothe tooth. As will be also appreciated, the relation between theilluminator assembly 80 and imaging subsystem 50 may be configured suchthat with a combination of a beam splitter as known in the art,illumination and capturing of light reflected from an object may both bedone normal to an object's surface.

As will be appreciated, other conventional illumination assemblies maybe substituted in the optical measurement instrument as the applicationrequires. The assemblies may also include polarizers that limit theeffect of specular gloss in the captured image.

Searchlight Illumination

The preferred embodiment of the optical measuring instrument usessearchlight illumination to illuminate objects during opticalcharacteristic measurements. As used herein, “optical characteristics”means characteristics such as color, shade, translucence, gloss and/orshape. “Searchlight illumination” means illumination wherein the objectmeasured is illuminated with constant irradiance. This definition ismore readily understood with reference to FIGS. 7 and 8. FIG. 7illustrates the constant irradiance phenomenon explained by J. Scheuchin his article, Modeling of Constant Irradiance Illumination System, pp.22–27, SPIE Vol. 3428 (1998), hereby incorporated by reference.

As explained, FIG. 7 depicts a collimated uniform light source 600. Thediameter of the integrating sphere exit port 620 is referred to asØ_(S), while Ø_(L) refers to the diameter of the collimating optic 628,here, a thin lens. The effective focal length of the optic is referredto as f. Any point on the exit port of the integrating sphere 620 willproduce a flux of collimated rays 640 a and 630 a to the right of thelens 628. The original light flux 630 and 640, formed by the top andbottom edges of the exit port 620 are shown. The shaded triangle 650 tothe right of the lens 628 represents the region, or cone, of uniformirradiance. Although depicted as a two dimensional triangle, it will beappreciated that the region is actually a three-dimensional cone. Ofcourse, depending on the aperture 620 and lens 628, the region ofconstant irradiance may take on cones of different shape as desired. Atany point within this region 650, normal to the optical axis 645,irradiance will be a constant value. At points outside of the cone, theirradiance will fall off as the distance from the cone increases. Theparaxial distance from the lens to the tip of the cone is referred to asthe critical distance Z_(c) and is given by:

$\begin{matrix}{Z_{c} = \frac{f\;\varnothing_{L}}{\varnothing_{S}}} & (2)\end{matrix}$At any point z along the optical axis where z<z_(c), the diameter of theuniform field Ø_(F) can be approximated by:

$\begin{matrix}{\varnothing_{F} = \frac{\left( {z_{c} - z} \right)\varnothing_{L}}{z_{c}}} & (3)\end{matrix}$

The region of uniform irradiance can be extended in length along theoptical axis 745 as illustrated in FIG. 8. By positioning the exit port720 at the focal of the achromatic doublet lens 738, the region ofuniform irradiance 760 may be extended a substantial distance along theoptical axis 745, as discussed in further detail below.

The advantage of searchlight illumination over conventional illuminationtechniques is illustrated in the graph of FIG. 9, entitled “IlluminationIntensity of Various Light Sources as Distance is Varied.” This graphillustrates the illumination intensity along the central axis from (a) atheoretical point source illumination 706, (b) conventional fiber opticilluminator 704, and (c) a searchlight source 702 used in the preferredembodiment. In the graph, the Y axis represents light intensity along acentral axis of the illumination sources projecting in the same inactionas the light is projected. The X axis represents the relative distancefrom the target, that is, the object measured, to each source.

As shown, the intensity along the central axis from the theoreticalpoint source 706 and fiber optic illuminator 704 is very strong when thetarget is near these sources; but that intensity rapidly decreases asthe relative distance from the source to the target increases. Incontrast, with a searchlight illuminator 702, which, by definition, hasconstant irradiance, the intensity along the optical axis remainssubstantially uniform at a distance within the operating range of theilluminator, as depicted by example here, from a relative distance ofabout 0.95 to about 1.0. At a distance somewhat greater than 1.05, theintensity from the searchlight gradually begins to decrease; but at arate much less than the theoretical point source 706 and theconventional fiber optic illuminator 704.

Of course, as the illumination source distance to target issignificantly increased (not shown on graph), even the searchlightillumination intensity will begin to decrease along the optical axis.But, for purposes of the carrying out the preferred embodiment of thepresent invention, illuminated targets or objects are positioned at apre-selected distance from the searchlight source so that they aresubstantially within the region of constant irradiance.

The graph of FIG. 9 and related data are exemplary only; targets placedat different relative distances from the light sources may beilluminated by the searchlight source differently than as depicted.Moreover, even though the illumination intensity apparently decreasesfor searchlight sources along a central axis at relative distancesgreater than about “1,” an object disposed at relative distances greaterthan 1 still may be considered to be illuminated within the region ofconstant irradiance. As used herein with reference to the presentinvention, “constant irradiance” means irradiance (or light) that issubstantially uniform in intensity in three dimensions; the X and Ydimensions, and the Z dimension, which is preferably axially alignedwith the central axis of a source of light. As used herein withreference to the present invention, “substantially uniform” means thatthe light preferably varies about ±4% in any of the three dimensions,more preferably about ±2% in any of the three dimensions, and mostpreferably about ±1% in any of the three dimensions.

The optical measuring instrument of the preferred embodiment usessearchlight illumination to illuminate an object while the object'soptical characteristics are measured. FIG. 5 generally depicts asearchlight illuminator and FIG. 10 depicts the searchlight illuminatoras it is configured in the preferred embodiment of the opticalmeasurement instrument.

With reference to FIG. 5, light fluxes 530 and 540 are projected throughexit port 520 of illumination source 518 which is depicted as anintegrating sphere, but may be any uniform diffuse source. The lightfluxes are projected onto lens 528 positioned at a pre-selected distanceM from the illumination source 518. Depending on the desired size of theregion of constant irradiance 560, this distance M is experimentallydetermined the light fluxes 530 and 540 transmitted through lens 528form a region of constant irradiance 560 including transmitted lightfluxes 530 a and 540 a The lens may, of course, be of any configurationcapable of forming regions of constant irradiance and need not belimited to the achromatic doublet lens depicted.

The searchlight illuminator 80, including source 518 and lens 528,preferably is placed a pre-selected distance D from the center of theobject for which optical measurements are to be collected. The center ofthe nominal object or target may be placed at about 50 millimeters toabout 100 millimeters from the lens, preferably from about 60millimeters to about 70 millimeters from the lens, more preferably fromabout 63 millimeters to about 67 millimeters from the lens, and mostpreferably, about 65 millimeters from the lens. This distance Destablishes a reference distance within which all points of the objectoptically measured are illuminated in the region of constant irradiance560. For purposes of taking optical measurements of teeth, it ispreferable to illuminate a substantial portion of the tooth or remainingteeth with the region of constant irradiance 560.

To establish distance D and insure that the points of the objectmeasured are within the region of constant irradiance, a spacer is usedto separate the illuminator 80 from the tooth. Preferably, a sanitaryshield, described in further detail below, is attached to the opticalmeasuring instrument that includes illuminator so that when the shieldis disposed against or adjacent to the tooth, the distance D isestablished and the tooth is positioned in the region of constantirradiance. As will be appreciated, the illuminator 80 is positioned sothat the light of the region of constant irradiance is reflected andcollected by the imaging subsystem of the preferred optical measuringinstrument described in further detail below.

With reference to FIG. 10, the preferred configuration of theilluminator 80 will now be described. The illuminator 80 generallyincludes light source 818 that is preferably a halogen lamp that emitswhite light. Of course, any conventional lamp, bulb or uniform anddiffuse light source may be used depending on the desired application.Preferably, the light source 818 is incorporated into a sub-housing 854that is removable from main housing 850 so that the light source 818 maybe replaced or serviced. Focusing reflector 810 focuses light from thelight source 818 through aperture 820 so that light rays are projectedonto lens 828. Optionally, the aperture 820 may include adjacent to it alight shaping diffuser 816 that provides even light distribution andhomogenizes light fluxes to provide uniform application in transmissionof light from the light source 818 to the lens 828. The preferred lightshaping diffuser is available from Physical Optics Corporation ofTorrance, Calif. Of course, any diffuser capable of homogenizing and/orenhancing the uniformity of light transmitted from a light source to alens may be used.

Light rays from light source 818 are projected through aperture 820whose size is determined by the desired application and distribution ofsearchlight illumination by the illuminator 80. The aperture optionallymay be covered by heat absorber 814 which is preferably in the form of aheat absorbing glass plate or synthetic material. The heat absorber 814absorbs excessive heat created by the light source 818. Of course, thisheat absorber 814 may be omitted in applications where there is noconcern of heat buildup.

Illuminator 80 also includes a light limiting stop 832 that preciselyconfigures the light from the aperture 820 on the lens 828. As will beappreciated, optical back scatter fins 852 are included in the housing850 to prevent excessive back scatter of light that may confound thelight transmitted by the light source 818 to the lens 828. Of course,the fins 852 may be colored, such as with a black or dark color tofurther reduce back scatter of light.

The illuminator housing holds lens 828 a predetermined distance fromlight source 818 to optimize the searchlight illumination projected fromthe illuminator 80. Of course, as discussed above in reference to FIG.5, the distance from the lens to the light source may be varied toobtain the desired searchlight illumination. The lens preferably is anachromatic doublet lens, but as will be appreciated, any lens capable ofproviding a region of constant irradiance at significant distances alongthe optical axis of the lens may be used.

With reference to FIG. 6, the illuminator 80 is configured in fixedrelation to the optical imaging subsystem 50 so that the illuminationreflected from the object measured is reflected back to the imagingsubsystem 50 for sensing and subsequent measurement of opticalcharacteristics of an object. In operation, the illuminator depicted inFIG. 10 performs in the same manner discussed above in reference to thegeneric illuminator of the present invention depicted in FIG. 5.

Imaging Subsystem

With reference to FIGS. 6 and 11 in the imaging subsystem 50 will now bedescribed. The imaging subsystem is in electrical communication with theprocessor 22 to enable transfer of optical characteristic data indigitized form collected by the imaging subsystem 50 to the processor20. The electric prongs 52 may be connected to a cable (not shown) thatprovides this electrical communication with the processor 20.Additionally, the connector 52 may be connected to an additional cable(not shown) that provides electrical communication with the power source90 to enable the operation of motor 54 and image sensor 56 depicted inFIG. 11.

With particular reference to FIG. 11 the preferred imaging subsystemincludes lens 58 mounted in cover 59; filter wheel assembly 60 rotatablymounted to and driven by stepper motor 54 which is mounted to supportplate 66; position sensor 62 for indexing rotation of the filter wheel60, and image sensor 56. The subsystem may optionally include aninfrared blocking lens 64 to prevent infrared bandwidths from reachingthe image sensor. All of these elements are aligned so that light L,reflected from a tooth, is transmitted through lens 58, one of thefilter elements 60 a–f, and the infrared blocker 64, ultimately impingeson and is captured or collected by the image sensor 56. The image sensor56 converts this light L to digitized form and transfers the digitizedform to processor 20.

Alternatively, the imaging subsystem may be configured so that thefilter assembly is positioned between an illumination source and theobject measured (not shown). In this manner, light from the illuminationsource would be transmitted through the filter assembly elements beforebeing reflected from the tooth; however, reflected light impinging: onthe image sensor would still be of bandwidths selectively transmitted bythe filter elements.

The lens 58 preferably has low chromatic aberration over the visiblelight spectrum from the 380 nm to 700 nm wavelength range. The lensfocuses light L toward the image sensor 56, and causes the light to betransmitted through the elements of the filter wheel 60 a–60 f in theprocess. The filter wheel assembly of the preferred embodiment is asector of 180 degrees including six elements. Of course, the assemblymay be of any shape and include any number of filter elements.

The filter wheel assembly 60 of the preferred embodiment includes filterelements 60 a–f, wherein filter elements 60 a–d are of pre-selected bandpass functions. “Band pass function” means information that is used tospecify how a filter absorbs specific wavelengths of light as thatlight, also referred to as “radiant flux,” is transmitted through amaterial. More preferably, filter element 60 a has a band pass functionthat permits it to transmit only X tristimulus value bandwidths andattenuate all other bandwidths; 60 b has a band pass function thatpermits it to transmit only Y tristimulus value bandwidths and attenuateall other bandwidths; 60 c has a band pass function that permits it totransmit only Z tristimulus value bandwidths and attenuate all otherbandwidths; and 60 d has a band pass function that permits it totransmit only X′ tristimulus value bandwidths and attenuate all otherbandwidths. These filters consistently attenuate bandwidths outsideselected bandwidths to less than about 1/40^(th), preferably less thanabout 1/100^(th), and more preferably less than about 1/1000^(th) of thevalue of the maximum transmittance of the filter. Of course, the filterelements 60 a–d may have any band pass function and attenuation asdesired, and they may be altered in number so that only a selectednumber of filters are used in measurement.

Optionally, the filter assembly 60 may include opaque element 60 e toestablish dark current information of the image sensor 56. Dark currentinformation is current that flows in an image sensor when no opticalradiation is impinging on the sensor. This current effectively distortsthe electronic signals transmitted by the sensor to the processor.Accordingly, it is preferred to measure this dark current informationand subtract it from the electronic signals generated during collectionof bandwidths transmitted to the sensor so that subsequent opticalcharacteristic measurements do not include this dark currentinformation. The filter wheel may also include an open element space 60f that transmits all light wavelengths to the image sensor. Transmittingall light wavelengths to the image sensor may be desired when initiallyacquiring an image of an object to help identify regions of the tooththat have high gloss.

With reference to FIG. 11, the filter is indexed with index 69 thatinteracts with position sensor 62 to synchronize the timing of imagingsensing by image sensor 56 and alignment of individual filter elements60 a–f over the image sensor 56. The position sensor may be a photodiodeposition sensor or any other sensor capable of sensing movement of thefilter wheel 60 via detection of the position of index 69. The positionsensor 62 is in electrical communication with the processor 20 so thatthe processor may initiate the stepper motor 54. Stepper motor 54sequentially rotates the filter wheel assembly in pre-selected angularincrements to position elements of the filter wheel 60 a–60 f over theimage sensor so that light is transmitted through the light transmittingelements to the image sensor 56.

The stepper motor 54 is mounted to the back of the support plate 66 in amanner that limits contamination, magnetic field interaction, and heattransfer from the motor to the image sensor 56. The stepper motorpreferably rotates the sectored filter wheel 60 in an indexed versusfree-spinning manner.

The image sensor 56 is preferably a complimentary metal-oxidesemiconductor (CMOS). As will be appreciated, any monochromatic sensoror photo detector may be substituted for the CMOS, including but notlimited to a charged coupling instrument (CCD) sensor. As will beappreciated, the image sensor collects or captures bandwidths of thelight L that is transmitted through respective filter elements 60 a–d,converts those functions to digitized form, and transfers the digitizedform, also referred to as electronic signals, to the processor 20.

The stepper motor 54 and image sensor 56 are all synchronized,preferably by the processor 20, so that the image sensor 56 collects thebandwidths transmitted through each filter element 60 a–d when thosefilters are aligned one by one over the image sensor 56. The positionsensor provides feedback via interaction with index 69 to the processor20 to initialize and deactivate the stepper motor 54 in a desiredmanner.

With reference to FIG. 11, the preferred operation of the imagingsubsystem will now be described. Light reflected from an object,preferably a tooth, travels pathway L through lens 58. Lens 58 focuseslight reflected from the tooth toward the image sensor 56. In so doing,selected bandwidths of the light L is transmitted through one of thefilter wheel elements 60 a–f. Each transmission of light L through anindividual filter, and each instance where no light is transmittedthrough the opaque element, and each instance when all light istransmitted through the open element is referred to as a “frame”. Thestepper motor 54 sequentially aligns each of the filter elements 60 a–60d and optionally the opaque and open filter elements 60 e and 60 f,respectively, over the image sensor 56. The image sensor 56 collects aframe when each filter element is placed over the sensors. Accordingly,in the preferred embodiment, the image sensor 56 collects, frame byframe, different tristimulus value bandwidths that are transmittedthrough the elements of the filter wheel 60.

The alignment of elements 60 a–f is controlled by stepper motor 54 whichis controlled by processor 20. In the preferred embodiment, when colormeasurement of light L reflected from a tooth is initialized, thestepper motor is in a “park” mode; that is, index 69 is aligned withposition sensor 62. During measurement, the processor directs thestepper motor to rotate from the park mode through a plurality ofpartial movements consequently turning the filter wheel assembly 60 aplurality of pre-selected angles. These angles are such that each filterwheel element 60 a–60 f is positioned over the image sensor so thatimage sensor 56 collects a frame of data for light transmitted througheach of the filter elements individually or for dark current into motionwhen element 60 e is positioned over the sensor. In this manner, onlyone bandwidth is transmitted to and captured by the image sensor at agiven time or in a single frame.

In the preferred embodiment, the image sensor 56 takes three colormeasurements of a tooth. Each measurement comprises nine frames of data,which are subsequently stored in a processor 20 and combined to form asingle measurement, or “image” of the tooth. Those frames represent twotransmissions of X bandwidths of light L through filter 60 a twotransmissions of Y bandwidths of light L through filter 60 b twotransmissions of Z bandwidths of light L through filter 60 b, twotransmissions of X′ bandwidths of light L through filter 60 d, and asingle dark current information frame when the opaque element 60 e ispositioned over the image sensor 56. This duplication of frames helps tointegrate over time the collected bandwidths and may provide data neededfor stabilization of the image.

As used herein, “stabilization” means combining the frames of datacollected at different points in time so that the resultant image doesnot indicate that the optical measuring instrument was moved between thepoints in time during which the frames were taken. Multiple framescollected by the sensor are separated in time because it takes a smallfraction of time to collect a first frame, through, for example, filterelement 60 a, move the filter wheel assembly 60 with the stepper motor54 and collect the next flame through, for example, filter element 60 b.During this small fraction of time, the operator of the opticalmeasurement instrument may accidentally move the instrument by rotatingor shaking it. Accordingly, the frame collected for one filter elementmay be slightly different from other frames and the frames will notmatch up point for point. To correct this, once the data is converted todigitized form by the sensor and communicated to the processor, theprocessor uses special algorithms to align the frames so that asubstantial number of points on one frame collected match up with asubstantial number of points on the other frames collected.

A flow diagram conceptually outlining the process of aligning frames isdepicted in FIG. 12. This process is preferably carried out by theprocessor of the instrument, but may alternatively be carried out by aseparate computer if desired. Aligning frames may begin with theselection of two or more images to be aligned 1002. A sub-region of bothimages containing the object desired is designated 1004. The brightnessof these designated images are normalized 1005. An initial inter-imagecorrelation value is calculated and a loop count is set to zero 1006. Atmacro step 1, a query is offered; is the inter-image correlation at anacceptable value 1008? If yes, the process skips to macro step 2 andstep 1030 where it returns final correlation value loop count, loopcount, row offset, column offset and angular rotation values. From thisstep, the process proceeds to done 1032.

If no is the response to query 1008, the process proceeds with step1010, where an error function that assesses column misalignment of thetwo images is calculated. In step 1012, one image is repositioned toremove column misalignment. In step 1014, an error function thatassesses row misalignment is calculated. In step 1016, correlation isassessed; if correlation has degraded, then row movement is undone. Instep 1018, one image is repositioned to remove row misalignment.Correlation is assessed in 1020; if it has degraded, then columnmovement is undone. An error function is calculated that assessesangular misalignment in step 1024. In step 1026, correlation isassessed. If correlation has degraded, then the rotation is undone.

In step 1028, a query is offered; has the loop been met? If yes, theprocess skips to macro step 2, and 1030, where it returns to finalcorrelation value loop count, loop count, row offset, column offset andangular rotation values. The process proceeds to being done 1032. Instep 1028, if the response is no, a inter-image correlation value iscomputed 1034; and the process skips to macro step 1 again to repeat allsteps as necessary any number of times so that the process proceeds todone 1032. Of course, the preferred process may be modified in sequence.Steps may be modified and/or selectively repeated. Different steps maybe added as well, depending on the desired application.

When the points of each frame are aligned with all the points of allother frames, the frames are collectively displayed to form an image ofthe object that reflected the light collected by the sensor. Preferably,a substantial number, if not all, of the points of this image willinclude all the tristimulus value bandwidths, that is the X, Y, Z and X′tristimulus bandwidths that were collected by the image sensor. Thisimage is preferably displayed on display 18 and stored in microprocessor20. The image may be downloaded from the microprocessor 20 to a personalcomputer. In embodiments where only tristimulus bandwidths are collectedby the imaging system, it will be appreciated that there is no need toperform lengthy calculations to derive tristimulus values if the outputof the system be in tristimulus value format.

As will be further appreciated, the bandwidths collected by the imagesensor may be combined and averaged in an image of the object intoregions of uniform bandwidths. It is also possible to arithmeticallycombine into color zones those adjacent image points where colordeviation between these adjacent image points do not exceed apredetermined value. In this way, measured tooth color can be subdividedinto several color zones having different colors or bandwidths. Themaximum number of such color zones in a prosthesis may be limitedbecause a dentist or restoration manufacturer usually subdivides aprosthesis only into a limited number of color zones.

In addition to matching points to stabilize and/or align the frames toform an image of the tooth, the processor may also detect measurementerrors if frames have been improperly collected. For example, if theoperator of the optical measurement instrument drastically rotates ormoves up and down or side to side the measuring instrument whilesequential frames are being collected, one or more of the collectedframes may be drastically different from the other. For example, oneframe may be of a tooth and the next may be of a gum due to the drasticmovement of the optical measuring instrument between frames.Accordingly, it would be difficult to align the points of one frame withthe corresponding points of other frames because the frames would bequite different.

In cases where the processor detects that the frames collected aresufficiently different from one another so that corresponding points ofdifferent frames cannot be matched to form an image of the tooth, theprocessor indicates to the operator that the measurement must be redone.This indication may be communicated via display means or any otherconventional alarm means. Accordingly, the operator retakes the opticalcharacteristic measurement of the tooth to collect satisfactory data. Asa result, the optical measuring instrument insures accurate and completeimages are collected for further processing and manufacture of dentalprosthesis.

Additionally, the processor preferably has the capability to store threeor more images of object. These images may be recombined or weldedtogether using appropriate welding software to combine multiple imagesinto a single image. For example, dentists may use welding software toarrange individual images downloaded from the optical measuringinstrument into a single image that replicates the configuration ofteeth surrounding a damaged tooth in a patient's mouth.

Sanitary Shield

The shield used in conjunction with the preferred optical measurementinstrument is generally depicted in FIGS. 13 and 14. The shield 300 isgenerally a hollow body having a tapered portion 320; however, thedimensions and size of the shield and its components may be varied fordifferent applications. The shield is preferably hollow so that itfreely transmits light through it, that is, first end 322 is in“illuminatory communication” with second end 310. Disposed at one end ofthe tapered portion is first end 310 that defines aperture 312. Theaperture 312 may be of any size depending on the illumination source andthe amount of light desired to be collected that is reflected from theobject measured. Reference color strips 330 border the edges of theaperture. These strips are adjacent the aperture or at least positionedso that they are in the image field 350. The image field is the fieldthat is included in an image that, is collected by an image sensor ofthe optical measurement instrument. The reference strips may be includedon the tapered portion 320 as long as they are included in collectedimages. Preferably, the color of the reference strips is off-white, butany color may be used, as long as the strip is of a known color.

In operation, the reference strip is included in the image field 350when the optical measurement instrument collects an image of an object.The measured reference strip values are compared to values acquiredduring instrument calibration. This comparison provides a method ofdetermining not only the lamp intensity variation, but also provides amethod to determine changes in lamp color temperature. Both of thesevalues must be known to provide accurate color measurement data from theimaged tooth. Lamp compensation factors are applied to all other objectsin the image field 350, such as a tooth to determine the true colors ofthose objects. A true color image of the object may then be producedfrom these true colors.

The interior of the shield's hollow body is preferably opaque orotherwise colored with a dark material that prevents ambient light onthe exterior of the shield from entering into the shield and pollutingthe data collected in the image field 350.

The shield 300 may also include indicia 340 disposed on first end 310.The indicia are preferably configured on end 310 so that it is includedin the image field 350 when an image is collected. These indicia may beof any type, but preferably indicates the origin, such as manufactureror distributor of the disposal shield to prevent counterfeiting thereof.The indicia 340 may also include patient information, a shield lotnumber, an expiration date, or any other information relevant to thepatient or the optical measuring instrument. The indicia may be printedon, included in, affixed to or otherwise associated with the shield inany conventional manner. For example, the indicia may be a printedadhesive label or a barcode.

In the preferred embodiment, the shield establishes a predetermineddistance to an object from an illumination source 80 or image sensor 56as depicted in FIG. 14. The length of the shield L is pre-selected sothat when aperture 312 is disposed adjacent to or in contact with theobject to be measured, for example the tooth T, the illumination source80 and image sensor 56 is a specific distance D from the object T.Accordingly, the precise illumination or sensing by the illuminator 80or sensor 56 may be duplicated in every measurement. This specificdistance is also pre-selected to prevent diffusion or scattering of thelight generated by the illumination source 80 by the time the lightreaches the aperture or object measured.

The shield 300 may be secured to the optical measuring instrument asdepicted in FIG. 17 in any convention manner. Preferably, the shieldincludes clips 324 that releasably clips to pegs 224 of the opticalmeasuring instrument. Of course, the shield may be secured to theoptical measuring instrument by any conventional fitting as theapplication requires.

As will be appreciated, the shield may be of paper or plastic or othermaterial which may be disposable, cleanable, reusable or the like inorder to address any contamination concerns that may exist in aparticular application. The shield may also be disposable or reusable.In the case of reusable shields, the shield is preferably constructed ofmaterial that can withstand sterilization in a typical autoclave, hotsteam, chemiclave or sterilizing system.

Line of Sight Viewing

FIGS. 15 and 16 illustrate the line of sight viewing of the preferredembodiment. The optical measuring instrument 10 includes housing 12 anddisplay 18 mounted therein. As explained above, an image sensor is alsoincluded in the housing 12. The image sensor collects images from animage sensor view 402, also referred to as “line of sensing.” The lineof sensing projects outward from the housing 12, through the installedshield 300 toward the object for which an image is to be collected, forexample the tooth 4. The object should be disposed in this line ofsensing 402 so that the optical measurement instrument may sense andmeasure the optical characteristics of the object.

Once the image sensor takes a measurement of the object in the line ofsensing 402, that measurement is processed by the processor of theinstrument (see FIG. 6) and transferred to the LCD 18. The LCD displaysthe data as an image thereon in the preferred embodiment. The image maybe magnified or reduced if desired. Of course, any conventional dynamicdisplay may be used in place of a LCD.

With the image displayed on the display 18, an operator 6 may view thedisplay along a line of viewing 400. This line of viewing 400 is alignedwith the line of sensing 402 so that the operator 6 views the tooth onthe display in the same perspective as the image sensor senses thetooth. Manipulation of the line of sensing 402 preferably corresponds toa different image being output on the display 18. For example, when anoperator moves the device, and consequently the line of sensing 402, tothe right of the tooth 4, the image output on the screen 18 willcorrespond to whatever object is to the right of the tooth. Morebasically, a user may manipulate the device to realign the line ofsensing by viewing an image on the screen without having to reverse orotherwise alter his normal thought process for acquiring and viewing animage.

With reference to FIG. 15, the display 18 is preferably aligned inparallel behind the image sensor 56 in housing 12. And preferably, thedisplay 18 is generally perpendicular to the line of sensing 402 and/orline of viewing 400. Of course, the screen 18, sensor 56, line ofsensing and line of viewing may be aligned in other configurations sothe line of viewing 400 is axially aligned with the line of sensing 402.

The optical measurement instrument 10 is configured in any way thatallows the operator to manipulate the instrument 10 and simultaneouslyview the same image that the sensor senses on a display on theinstrument without periodically having to look away from the display andrealign the image sensor's line of sensing. Accordingly, the operatormay view the display alone along line of viewing 400 to precisely alignthe line of sensing 402 so that the instrument collects the image of thetooth as desired.

Sealed Unit

With reference to FIGS. 16 and 17 the optical measurement instrumentgenerally includes housing 12, divided into subparts 12 a and 12 b,display 18 and window 230. With particular reference to FIG. 17, thefront portion of the housing 12 defines aperture 240 covered by window230. The aperture allows illumination to be projected out from theinterior of the housing 12 and allows light reflected from an object toenter back into the housing 12 and be sensed by an image sensor (notshown). The aperture 240 may be of a variety of configurations and sizesthat facilitate illumination and sensing characteristics as desired.

The aperture is circumferentiated by an internal lip 210 that ispreferably formed as part of the housing 12. Disposed over the lip iswindow or cover panel 230. Preferably, this cover is made from plastic,glass or other synthetic material that allows high efficiencytransmission of light through it. Disposed between the lip 210 and thewindow 230 is seal 220. The seal may be any gasket or seal, for examplea sealing adhesive, that prevents “pollutants”—meaning dust, dirt,debris, moisture, cleaning agents, and chemicals—from entering theinterior of the housing body 12 through or around the aperture 240.

The display 18 is preferably sealed to or into the housing 12 in amanner that prevents pollutants from entering the interior as well. Itis preferred that the display is touch sensitive and is able to providea means to control and operate the device. In this manner, no difficultto clean around external buttons are included in the housing.

Subparts 12 a and 12 b are preferably seated together in a manner thatalso prevents pollutants from entering the interior of the housing bodyalong the portions of the subparts where the subparts connect to or seatagainst one another.

As explained, all of the above elements, the sealed window 240, themated subparts 12 a, 12 b, and the display 18, prevent pollutants fromentering the interior of the device when the pollutants come in contactwith the device, such as when the device is wiped down with cleaning orsterilizing agents, or when the device is dropped on a dirty floor.However, these elements do not significantly prevent the pollutants fromentering the interior of the device if the device is fully submersed inpollutants, for example, if the device is submersed in liquid cleaningagents.

The device of the present invention in some embodiments may include aport 22 or other connection for communication with a docking station(FIG. 18), computing device and/or power source (not shown). Typically,it is difficult to seal this port to prevent pollutants from enteringthe interior of the housing 12.

The optical measurement instrument is easily sanitized and/orsterilized. Users may clean it by wiping it down without significantworry of leaking sanitizing or sterilizing agents or other cleaningagents into the interior of the housing 12, a consequence thatpotentially might damage the internal components of the instrument. Ofcourse, care must be taken to prevent excessive exposure of a connectionor port to pollutants to prevent those pollutants from entering theinterior of the device. In periods of non-use, or use in dusty regions,the risk of dust or debris entering the housing is significantlydecreased.

Dental Prosthesis Manufacture

The preferred process of creating a dental restoration or prosthesisfrom optical measurements taken from a damaged tooth or surroundingteeth will now be described. To begin, a dentist uses the preferredoptical measuring instrument to measure the optical characteristics of atooth or teeth that surround an area that was previously occupied by atooth. These optical measurements are converted to an image or pluralityof images in the optical measurement instrument. The images may bedownloaded from the optical measurement instrument to a computer wherethey may be stored. Of course, the image may be stored in anyappropriate electronic file format. Once the image is stored in thecomputer, it forms what is referred to as a restoration file. From thisrestoration file, the measured optical characteristics may bemathematically manipulated by the computer to be viewed as an averagecharacteristic map, as a grid of individual characteristics, as acontoured characteristic map, or any other desirable format as will beappreciated by those skilled in the art.

Next, the dentist transmits the restoration file to a restorativeprosthesis-manufacturing laboratory with any acceptable means.Preferably, however, the file is forwarded using electronic networkcorrespondence.

At the lab, a technician downloads the restoration file to reconstructthe patient's mouth, and in particular, the new prosthetic replacementfor the damaged or missing tooth. Software capable of thisreconstruction is available from X-Rite, Incorporated of Grandville,Mich. After the technician creates the restorative prosthesis, an imageof the prosthesis, preferably with the optical measuring instrument ofthe preferred embodiment.

The image of the prosthesis is inserted into an image of patient's mouthderived from the restoration file to determine quality and accuracy ofthe restoration. This may be done in several ways. First, the technicianmay use her own optical measuring instrument to take measurements of theprosthesis to create an image of the prosthesis also referred to as“prosthesis data.” She then takes this image and inserts it into animage of the patient's mouth taken from the restoration file. Of course,the technician may also compare the prosthesis data to the image of theoriginal tooth, if one exits. The technician conducts a comparison ofthe image of the tooth to the image of the patient's mouth or damagedtooth before the restoration is shipped from the lab. The technician maythen determine the quality. and accuracy of the restoration and decidewhether or not to ship it to the dentist for installation in thepatient's mouth.

In a second alternative embodiment, the technician may use the opticalmeasuring instrument to take measurements of the prosthetic restorationto create an image of the prosthesis and send that image to the dentist.The dentist may then visual insert the new tooth image into an existingimage of the patient's mouth to determine the quality and accuracy ofthe restoration. Based on his or her own judgment, the dentist may thencontact the lab to confirm or decline, the restoration. In cases wherethe restoration is confirmed, the lab will ship the restoration to thedentist for installation in the patient's mouth. In cases where thedentist declines the restoration because it is not an acceptable match,the lab constructs another restoration and takes a new image of thatrestoration. The new image is forwarded to the dentist to compare thatnew image to the image of the damaged tooth. This process may berepeated until an accurate restoration is created.

In a third alternative embodiment, the technician may simply create theprosthesis and send it to the dentist. The dentist uses her own opticalmeasurement instrument to obtain an image of the prosthesis. Thatprosthesis data is visually inserted into an image of the patient'smouth or compared to an image of the damaged tooth to determine thequality and accuracy of the restoration. If the restoration isacceptable, the dentist will install it in the patient's mouth. If therestoration is unacceptable, the dentist may request the lab to createanother restoration or alter the restoration in a manner to make it anaccurate duplicate of the original tooth for which it was designed toreplace.

Docking Station

With reference to FIG. 18, the optical measurement instrument 10 docksor rests in docking station 14 when not in use or when downloadingimages from the instrument 10 to a computer (not shown) connected to thedocking station for further analysis of these images or to forward thoseimages to a third party. The docking station 14 includes support 15 tohold the instrument 10 in a ready-to-grasp position; The instrument alsorests in port 24 that includes a plug (not shown) to interface withportal 22 (see FIG. 6) for download of images and recharging of powersource 90 of the instrument 10. The docking station may also provide adata connection for download/upload of patient information and/ordownload/upload of image and modified patient information to/from theinstrument 10. Of course any other information as desired may bedownloaded/uploaded.

In an alternative embodiment, the instrument may include a transmitterand/or receiver so that it can communicate with another instrument, witha docking station and/or directly with a computing device using awireless connection wherein data may be transported through radiofrequencies, light modulations, or other remote wireless communicationmeans.

The above descriptions are those of the preferred embodiments of theinvention. Various alterations and changes can be made without departingfrom the spirit and broader aspects of the invention as defined in theappended claims, which are to be interpreted in accordance with theprinciples of patent law including the doctrine of equivalents. Anyreferences to claim elements in the singular, for example, using thearticles “a,” “an,” “the,” or “said,” is not to be construed as limitingthe element to the singular.

1. An apparatus for creating an image of an object comprising: means forilluminating the object with illumination rays so that the objectreflects reflected rays; a monochromatic image sensor; means fortransmitting X, Y, Z and X′ tristimulus bandwidths included in at leastone of the illumination rays and the reflected rays, whereby the imagesensor collects a plurality of time-separated frames, each frameassociated with one of the tristimulus bandwidths; and means forcombining said plurality of frames to create an image of the object. 2.The apparatus of claim 1 comprising means for aligning a plurality ofpoints on a first frame with a plurality of points on at least a secondframe to form a plurality of aligned points.
 3. The apparatus of claim 2wherein said image includes said plurality of aligned points, each ofsaid aligned points including the tristimulus bandwidths transmitted bysaid transmitting means.
 4. An apparatus for measuring the opticalcharacteristics of an object illuminated with incident light andreflecting reflected light comprising: means for transmittingtime-separated tristimulus bandpass functions of at least one of theincident light and the reflected light; an image sensor for collectingsaid time-separated tristimulus bandpass functions of the reflectedlight; and a processor to combine and align said time-separatedtristimulus bandpass functions into an image representative of theoptical characteristics of the object.
 5. The apparatus of claim 4wherein said image sensor is a monochromatic sensor chosen from a CCD ora CMOS.
 6. The apparatus of claim 5 wherein said transmitting means is atranslatable tristimulus filter that transmits said tristimulus bandpassfunctions.
 7. The apparatus of claim 6 comprising means to synchronizethe translation of said tristimulus filter and the collection of saidtristimulus bandpass functions.
 8. The apparatus of claim 7 comprisingmeans to display the image in a line of view of an operator of theapparatus whereby the operator can view the image from a sameperspective as that which the image sensor collects said tristimulusbandpass functions.
 9. The apparatus of claim 5 comprising wirelessmeans to download information related to said image to at least onechosen from a docking station and a computing device.
 10. The apparatusof claim 5 comprising wireless means to upload information related to atleast one chosen from a docking station and a computing device.
 11. Aninstrument for acquiring a color image of a tooth comprising: a housing;a light source within said housing providing illumination of the tooth;an image sensor within said housing for acquiring an image of the tooth;and tristimulus filter means for selectively filtering the image of thetooth, said filter means including a plurality of tristimulus filters,said filter means further including means for moving said filterssequentially in alignment with said image sensor so that said imagesensor acquires time-separated images of the tooth, each time-separatedimage including pre-selected tristimulus information; and processormeans for combining the time-separated images into a single color image.12. A method for determining the optical characteristics of an objectcomprising: illuminating the object with incident light so that light isreflected from the object; filtering at least one of the incident lightand the reflected light; imaging the reflected light to form a pluralityof frames, each frame corresponding to at least one tristimulusbandwidth; and combining the plurality of frames to create an image ofthe object including optical characteristic data.
 13. The method ofclaim 12 wherein said combining includes aligning a plurality of pointson a first frame with a plurality of points on at least a second frameto form a plurality of aligned points.
 14. The method of claim 13wherein the image includes the plurality of aligned points, each of thealigned points including information from all the frames.
 15. A methodfor creating an image of an object, the object illuminated withillumination rays, the object reflecting reflected rays, comprising:transmitting a plurality of time-separated X, Y, Z and X′ tristimulusbandwidths of at least one of the illumination rays and the reflectedrays; collecting a frame for each of the time-separated tristimulusbandwidths; and combining the frames into an image including a pluralityof points, each of the points having data representative of each of theframes.
 16. The method of claim 15 wherein said transmitting is carriedout by disposing a filter that transmits a tristimulus bandwidth betweenthe object and a source of illumination whereby light from theillumination source is transmitted in a plurality of time separatedtristimulus bandwidths to said object and said object reflects said timeseparated tristimulus bandwidths.
 17. The method of claim 15 whereinsaid transmitting is carried out by disposing a filter that transmits atristimulus bandwidth between the object and a sensor that carries outsaid collecting step whereby light reflected from the illuminated objectis transmitted in a plurality of time separated tristimulus bandwidthsto the sensor.
 18. The method of claim 16 comprising displaying theimage in a line of view whereby an operator of the apparatus can viewthe image from a same perspective as the time separated bandwidths arecollected.
 19. The method of claim 17 comprising displaying the image ina line of view whereby an operator of the apparatus can view the imagefrom a same perspective as the time separated bandwidths are collected.20. The method of claim 16 wherein the filter includes a plurality offilters chosen from X tristimulus bandwidth transmitting filters, Ytristimulus bandwidth transmitting filters, Z tristimulus bandwidthtransmitting filters, and X′ tristimulus bandwidth transmitting filters.21. The method of claim 17 wherein the filter includes a plurality offilters chosen from X tristimulus bandwidth transmitting filters, Ytristimulus bandwidth transmitting filters, Z tristimulus bandwidthtransmitting filters, and X′ tristimulus bandwidth transmitting filters.22. The method of claim 20 wherein said collecting is carried out with amonochromatic image sensor.
 23. The method of claim 21 wherein saidcollecting is carried out with a monochromatic image sensor.
 24. Themethod of claim 15 comprising downloading with wireless communicationinformation chosen from the image, information related to the image andpatient information to a computing device.
 25. The method of claim 15comprising uploading with wireless communication information chosen fromthe image, information related to the image and patient information to acomputing device.